This invention generally relates to multi-layered golf balls, and more particularly the invention relates to golf balls having a core with at least three layers.
Generally, golf balls have been classified as wound balls or solid balls. Wound balls are generally constructed from a liquid or solid center surrounded by tensioned elastomeric material. Wound balls are performance golf balls, and have a good resiliency, spin characteristics and feel when struck by a golf club. However, wound balls are generally more difficult to manufacture than solid golf balls.
Early solid golf balls were generally two piece balls, i.e., comprising a core and a cover. The primary purpose of the core is to be the xe2x80x9cspringxe2x80x9d of the ball or the principal source of resiliency. The cover protects the core and improves the spin characteristics of the ball. More recently developed solid balls comprise a core, a mantle layer and a cover to improve the playing characteristics of the balls.
Solid balls are typically made with a single-solid core, usually made of a cross-linked polybutadiene or other rubber, which is encased by a cover. These balls are typically the least expensive to manufacture as the number of components is low and these components can be manufactured by relatively quick, automated molding techniques.
The prior art also discloses golf balls that have been designed to provide particular playing characteristics. These characteristics include the initial velocity and spin of the golf ball, which can be optimized for various types of players. For instance, certain players prefer a ball that has a high spin rate in order to control and stop the golf ball. Other players prefer a ball that has a low spin rate and high resiliency to maximize distance. Generally, a golf ball having a hard core and a soft cover will have a high spin rate. Conversely, a golf ball having a hard cover and a soft core will have a low spin rate. Golf balls having a hard core and a hard cover generally have very high resiliency for distance, but have a hard feel and are difficult to control around the greens.
The prior art also discloses golf balls with multi-layered core, such as U.S. patent application Ser. No. 2002/0019268, which discloses a six-layer core with an inner core layer having a low modulus of elasticity and an outer core layer having a high modulus of elasticity. Golf balls with two-layer core are also known, such as U.S. Pat. No. 6,245,859 B1, 6,213,895 B1 and 6,057,403, among others. Similarly, golf balls with three-layer core are disclosed in U.S. Pat. Nos. 5,772,531 and 5,743,816. However, none of these references discloses multi-layered golf ball core with predetermined thickness ratio among all the core layers.
The invention is directed to a golf ball comprising a core and a cover, wherein the core comprises at least three layers and wherein the radius and the thickness (T) of the core layers follow the equation TAxe2x89xa72TBxe2x89xa74TC, wherein TA is the radius of the inner most core, TB is the thickness of the adjacent outer core layer and TC is the thickness of the next adjacent outer core layer.
The golf ball may further comprises a fourth core layer, and the radius and thickness (T) of the core layers follow the equation TAxe2x89xa72TBxe2x89xa74TCxe2x89xa78TD, wherein TD is the thickness of the next adjacent outer core layer. The golf ball may further have a fifth core layer, and the radius and thickness (T) of the core layers follow the equation TAxe2x89xa72TBxe2x89xa74TCxe2x89xa78TDxe2x89xa716TE, wherein TE is the thickness of the next adjacent outer core layer. Additionally, the golf ball may further comprises a sixth core layer, and the radius and thickness (T) of the core layers follow the equation TAxe2x89xa72TBxe2x89xa74TCxe2x89xa78TDxe2x89xa716TExe2x89xa732TF, wherein TF is the thickness of the next adjacent outer core layer.
In accordance with another aspect of the present invention, one of the core layers can be a water vapor barrier layer, and the water vapor barrier layer can be a compressed exfoliated graphite layer. Additionally, one of the core layers can be a thin dense layer, and/or a perforated spherical shell. One of the core layers may be capable of absorbing shock, and/or comprises substantially no fillers. One of the core layers may be foamed.
In accordance with another aspect of the present invention, the core layers have progressively decreasing hardness from the innermost core layer toward the outermost layer, and wherein the hardness of the innermost core layer is at least 15 points on the Shore D scale higher than the hardness of one of the outer core layers. Alternatively, the core layers have progressively increasing hardness from the innermost core layer toward the outermost layer and wherein the hardness of the innermost core layer is at least 15 points on the Shore D scale lower than the hardness of one of the outer core layers.
At least one core layer comprises polybutadiene, a crosslinking agent, a co-crosslinking agent, and a cis-to-trans catalyst, and the cis-to-trans catalyst is preferably a halogenated organo-sulfur compound.